There is a huge need for integrated manufacture of multi-material and macro/micro/nano multi-scale structures in the fields of new materials (composites, metamaterials, functionally graded materials, porous lightweight materials, smart materials, nonhomogeneous materials, etc.), tissue engineering, biomedicine, MEMS, 4D printing, electronic products, flexible electronics (wearable electronic devices, etc.), aerospace, automobiles, etc. For example, in the biomedical field, in order to print a device including both a flexible material capable of moving along with knees and rigid electronic elements, a 3D printer should uninterruptedly perform all the following tasks: seamless transition from a flexible material to a rigid material, circuit printing using inks with various conductivities and resistances, and precise switching between the various ink print materials. To achieve such a capability of integrating different materials and properties in a printed product, the printing of the product requires a multi-material and multi-scale 3D printing process. In addition, implementations of function-driven integrated design and manufacturing of materials, structures, and functional components, and form control and performance control techniques in 3D printing also need powerful support from multi-material and multi-scale additive manufacturing techniques and devices.
However, most of the existing 3D printing processes employ single-material printing, and even some existing multi-material 3D printing processes are mainly based on the multi-printhead technique. Nevertheless, the processess based on multiple printheads have many shortcomings and limitations: (1) active mixing of multiple materials can not be achieved; (2) accurate control on various components of the multiple materials can not be achieved; (3) seamless transition between the multiple materials (e.g., seamless transition from a flexible material to a rigid material) can not be achieved; (4) the configured number of printheads and the number of types of printable materials are limited; (5) structures with multiple printheads and operations thereof are complicated, and the device cost; (6) frequent switching is required between printheads, leading to low printing efficiency; (7) it is difficult to print with high-viscosity liquid materials, leading to limit to the types of materials available for printing; (8) it is difficult to achieve macro, micro and nano cross-scale/multi-scale integrated manufacturing; and (9) the performance control in 3D printing is very poor. In addition, printheads for multiple materials generally include a plurality of printheads installed at the same height in parallel, wherein each printhead may handle one material, and typically, only one printhead operates during printing, and other standby printheads at the same height may interfere with constructing a tissue forming surface. Hence, it is difficult to achieve integrated manufacturing of multi-material and multi-scale structures using the existing 3D printing techniques.
Micro-scale 3D printing based on electrohydrodynamics (EHD) (Electronic Jet Printing), which is also referred to as electrohydrodynamic jet printing (E-jet), is a novel micro/nano-scale 3D printing technique emerging in recent years. It is a micro-droplet jet forming and deposition technique based on electrohydrodynamics (EHD). Different from the traditional jet printing techniques (hot jet printing, piezoelectric jet printing, etc.) with a “pushing” mode, EHD jet printing adopts electric field driving to generate very fine jets from the top end of a liquid cone (Taylor cone) in a “pulling” mode. As the electronic jet printing adopts a mode of drop-on-demand jet printing in the cone-jet mode, very uniform droplets can be generated and patterns with high precision can be formed; moreover, the print resolutions are not limited by the diameters of nozzles, and complex three-dimensional micro/nano structures can be manufactured with submicron-scale and nano-scale resolutions on the premise that the nozzles are not prone to blocking. Furthermore, a very extensive range of materials may be available for the electronic jet printing, ranging from insulating polymers to conducting polymers, from suspensions to single-walled carbon nanotube solutions, from metal materials and inorganic functional materials to biomaterials, etc. Therefore, compared with the existing 3D printing techniques, the present invention has already shown outstanding advantages and potentials in the aspects of cost, efficiency, controllability, print area (in connection with the roll-to-roll process), etc., and also has the characteristics of good compatibility (an extensive range of suitable materials, and particularly many high-viscosity materials), simple structure, and high resolution, and especially, has the particularly prominent potential in multi-material and cross-scale 3D printing. However, the existing multi-material electronic jet printing is mainly based on a multi-printhead solution with the shortcomings and limitations of the existing multi-printhead solution.
Hence, to overcome the shortcomings and drawbacks of the existing 3D printing and additive manufacturing in the aspect of integrated manufacturing of multi-material and macro/micro/nano multi-scale structures and to achieve “function-driven integrated seamless integration of structures, materials and performance design and manufacturing”, design elements, such as materials, microstructures, macrostructures, and the like, are combined with functional requirement goals to achieve form control and performance control manufacturing (especially improvement and optimization of the performance of products through the use of multiple materials and microstructure arrangements to add new functions) of complex tissue structures and meet the practical requirements of research and development and mass production in the aspects of new material development, biomedicine, electronic products, tissue engineering, MEMS, wearable electronic devices, 4D printing, etc. Then, there is an urgent need for development of a new process and equipment for multi-material and multi-scale 3D printing.